It was supposed to have been a small side event at the Copenhagen climate conference but it quickly turned into an ugly slanging match that eventually had to be resolved by burly security guards escorting one of the protagonists from the room.

It was supposed to have been a small side event at the Copenhagen climate conference but it quickly turned into an ugly slanging match that eventually had to be resolved by burly security guards escorting one of the protagonists from the room.

But for Stephen Schneider, a veteran climatologist, it was yet more evidence of the deeply divisive nature of climate science.

Schneider, a professor at Stanford University in California, had gone to Copenhagen to publicise his latest book, Science as a Contact Sport, but his press conference was soon hijacked by a little-known film-maker and climate sceptic who pressed him persistently about the emails leaked from the University of East Anglia's Climatic Research Unit.

As the title of his book suggests, Schneider is not someone who shies away from confrontational situations. He explained at some length, and with some vigour, why he could not comment on stolen, redacted emails taken out of context – especially to someone with a track record of using his quotes out of context.

The heated exchange continued after the press conference was formally over and was only resolved with the intervention of UN security guards. A heavily edited clip can be seen on YouTube. The sceptic comes over as a heroic seeker of truth, while Schneider is portrayed as the tricky, evasive scientist relying on a team of hired heavies to shield him from difficult questions.

The confrontation is just one example of the new uncomfortable world in which climate change scientists and campaigners now find themselves working in.

After more than 20 years of battling to achieve a global consensus on man-made warming, in a matter of weeks the sceptics are once again on the ascendant. And the most galling part about it – it was the mistakes, hype and hubris of some of the movement's most celebrated champions that have been responsible.

It started when copies of more than 1,000 emails dating from between 1996 and 2009 were stolen from a back-up computer at the University of East Anglia sometime prior to November 2009. Although there is no evidence that any of them alter the fundamental science of climate change, they do appear to show that scientists, especially the beleaguered head of the unit, Professor Phil Jones, were prepared to conspire together to delete information rather than release it.

That was enough to provide invaluable ammunition for climate sceptics. They showed the lengths that some of the most renowned climate scientists were willing to go to prevent their data and email correspondence from getting into the hands of the sceptic community. Their unwillingness to open the books on their science have been a huge own-goal because they suggest some kind of cover-up and, even worse, a subversion of the hallowed scientific process of peer review.

Schneider, one of the first scientists to warn about the rise in man-made greenhouse gases, said that by far the most frequent questions he gets asked right now concern the stolen East Anglia emails, even though they do not alter the basic science of climate change. "Nothing scientifically has changed because of any of this. The only changes are political and perceptual," he said.

Professor Julia Sligo, chief scientist at the Met Office, said: "With all the furore over the past few weeks it's very easy for the public to lose sight of these basis facts. CO2 levels are 30 per cent higher than at any time over at least the last 600,000 years and the rate of rise is unprecedented. Yes, there is uncertainty in the observations. We accept that and we quantify that, but it does not alter the message. I believe the case for anthropogenic global warming is very compelling and I think it's good for us to remind ourselves of that in the face of all these attempts to suggest otherwise."

An independent inquiry led by Sir Muir Russell is investigating the emails to see if there is any evidence of scientific misconduct. His report is not expected to be published before spring. Yesterday, a parallel investigation by Pennsylvania State University found that one of its top scientists, Professor Michael Mann, who was involved in many of the email exchanges with Professor Jones, was not guilty of scientific misconduct.

In the meantime, scientists in Britain said that they feel unable to address public concerns raised by the emails because of the problem of not knowing the bigger picture that lies the correspondence.

"What you have to understand is the context of those emails and we won't know that until the review is published," Professor Sligo said. "Anything taken out of context can look very damaging, so it's not the right time to comment on individual emails when we don't know the history of the discussion or the context in which they were written."

But it is not only the East Anglian scientists that have had a blow to their reputation. Perhaps even more damaging for climate science has been the admission by the widely renowned Intergovernmental Panel on Climate Change (IPCC). Earlier this month, the august UN body was forced to admit that it got it wrong over a claim in one of its 2007 reports suggesting that the Himalayan glaciers may have melted away by 2035.

It emerged that the claim came from a non-peer reviewed report by the WWF (formerly the World Wildlife Fund), who took it from a magazine article. The scientist behind the magazine's claim has since said that his comment, quoted accurately, was "speculative".

Rajendra Pachauri, the head of the IPCC, was told about the error last year but at that time dismissed suggestions that the claim was wrong, saying that the doubts were "voodoo science". The IPCC finally published a correction last month, but Pachauri has refused to apologise personally. John Sauven, the head of Greenpeace, yesterday questioned his judgement, saying he should have acted sooner.

The waters were muddied further at the weekend when it emerged that a report by the UN watchdog that global warming might wipe out 40 per cent of the Amazon rainforest had been based on a claim by green campaigners.

Sir John Houghton, a distinguished climate scientist who was lead editor of the first three IPCC reports, said that the body needs to do a lot more to improve its tarnished image. "There is a problem in public confidence and the IPCC and climate scientists really need to make sure their message it getting across in a more effective way," Sir John said.

"I don't think the climate scientists involved with the IPCC have done a good enough job of explaining what they have done. It's not just the public, it is scientists in fields other than climate research who wonder if there is any truth in what is being said," he said.

Or, as Kelvin MacKenzie, former editor of the The Sun, put it in his column read by millions: "I'm delighted to report that going up in smoke on the global warming bonfire are the careers of lying professors, deceitful glaciologists, rainforest racketeers, and our old friends the bandwagon politicians. Never felt happier – don't believe a word they say."

Climate change: The facts on the ground, and in the air

*Mountain glaciers

Most glaciers around the world are melting and there is a scientific consensus that many of these glaciers are probably melting faster now than in previous decades. However, some glaciers are expanding because of heavier snowfall at higher, colder altitudes, which may in itself be the result of warmer temperatures. The claim in the 2007 fourth assessment report of the IPCC suggesting that Himalayan glaciers would have melted by 2035 was an error of its working group 2, which dealt with "impacts". The section on Himalayan glaciers by the scientific report of working group 1 did not make the same mistake.

*Global temperature record

One of the oldest criticisms of the global temperature record, as monitored by thousands of weather stations around the world, is that it has not taken into account the effect of growing cities. A weather station situated in a city is going to experience the "heat-island effect" and will give higher readings than a comparable weather station a few miles away in the country. Climate scientists have repeatedly stated that they have taken into account the effect of growing urbanisation which may have influenced the recordings of some weather stations suffering urban encroachment.

*Sea level rise

Most of the observed rise in global sea levels in recent decades has been attributed to thermal

expansion of the warmer oceans – as water warms, it expands. But melting glaciers and ice sheets will also contribute to sea levels. The IPCC's 2007 report predicted that global average sea levels could rise by up to 59cm by 2100, but this estimate was widely criticised by some scientists as too conservative. The IPCC scientists deliberately omitted predictions based on melting ice sheets because of uncertainties in the science. Experts have since suggested that sea level rise could be twice as much as previously thought.

*Amazon forest

A number of studies have investigated what happens to tropical forests in a warmer world. One of the greatest fears is that as temperatures rise, so does the risk that something catastrophic may happen to the Amazon. The IPCC suggested that in a warmer world, 40 per cent of the rainforest of the Amazon could disappear. But it cited a report by green activists rather than the original study published in a peer-reviewed journal. However, the IPCC said it is had valid reasons for not changing the text of the report.

*Extreme weather

Climate modellers have predicted that there could be more "extreme events", such as storms and droughts, as a result of rising global temperatures. In a warmer world there could be more frequent or intense hurricanes, but there is still a great deal of scientific uncertainty. The IPCC has been criticised for incorrectly linking global warming with the severity and frequency of costly floods and hurricanes. However, the IPCC dismissed the criticism, saying that its entire report should not be judged on just one section. The IPCC said it clearly stated that one study detected an increase in economic losses due to extreme events but that other studies had not detected such a trend.